TWI558099B - Automatic quadrature network with phase and amplitude detection - Google Patents

Description

Auto-orthogonal network with phase and amplitude detection

The present invention relates to orthogonal frequency converters, and more particularly to automatic quadrature networks having phase and amplitude detection to simultaneously eliminate phase and amplitude errors in the output of the frequency converter.

The quadrature (I/Q) frequency converter relies on having a pair of mixers that are driven by quadrature local oscillator signals (i.e., two signals of the same frequency but 90 degrees out of phase). One of the simpler ways to achieve this desired result is to input a single frequency into a path with two phase shift paths (one of which is a series resistor followed by a parallel capacitor (RC); and the other The path is an orthogonal network of series capacitors followed by a path of parallel resistors (CR). If the resistances are equal and the capacitances are equal, then for a single frequency input, there is a particular frequency, wherein the outputs of the two paths are equal amplitude and quadrature. Outside of this particular frequency, although the phase relationship is maintained, the amplitude changes.

A method of generating an orthogonal signal from a local oscillator (LO) Using an amplitude detector and a feedback control loop, the feedback control loop adjusts the resistance or capacitance values in the RC and CR paths until the amplitudes of the orthogonal signals match. This method is exemplified by U.S. Patent No. 5,644,260 (DaSilva) and British Patent No. 1,345,274 (Ratzel). However, this approach does not produce perfect phase quadrature and equal amplitude when the invariant components of the network do not match, when the variable components are not accurately tracked, or when parasitic components are present. For example, because some non-ideal components (R is too large or too small compared to other components, or C has the same problem, etc.), the frequency of the RC circuit in an orthogonal signal path is too low, and The frequency of the CR circuit in an orthogonal signal path is too high. Figure 1 is a graphical representation of the DaSilva implementation showing that at the specified frequency (100 MHz (million Hz)), the amplitudes of the orthogonal signals are equal, but the phase difference between the two orthogonal signals is over the entire spectrum. Change, in this example, at an LO frequency of 100 MHz, the phase difference is 100° instead of 90°. In order to achieve an appropriate phase relationship, the static Vcal signal is used in conjunction with the detected amplitude, which is selected from the frequency table of the particular local oscillator signal input. However, due to time and temperature, this Vcal signal does not cause dynamic changes to the network, so the network requires frequent corrections or there is always some phase error present.

If the amplitude match does not exist, the alternative method uses a phase detector and a feedback loop to adjust one quadrature (RC) path or another orthogonal (CR) path until a perfect phase is orthogonal, as if U.S. Patent No. 4,908,532 (Chadwick) is exemplified. However, although this The signal passes through the stages, but ignoring the amplitude match causes the amplitude error. Since the phase difference will be 90° during a wide range of amplitude differences, one side or the other side will be so in urgent need of the signal that the limiting amplifier cannot be limited. Since the local oscillator levels are not the same at the input of these mixers, this results in a poor match between the two mixers.

What is desired is an auto-orthogonal network of orthogonal frequency converters that provides equal amplitude and ideal quadrature phase for the quadrature signals derived from the local oscillator.

Accordingly, the present invention provides an automatic quadrature network with phase and amplitude detection that provides equal amplitude and ideal quadrature phase for the quadrature signals derived from the local oscillator. The RC circuit provides one orthogonal path and the CR circuit provides another orthogonal path. The output from the RC/CR circuit is sensed to generate an amplitude control signal. These outputs are also limited in amplitude and detect the phase between the outputs at the limiter output to produce a phase control signal. The amplitude control signal and the phase control signal are combined to generate respective control signals of the RC/CR circuit, and the RC/CR circuit is automatically calibrated such that the orthogonal signals are of equal amplitude and ideal quadrature phase.

The objects, advantages, and other novel features of the invention are apparent from the description and appended claims.

12‧‧‧First variable resistor

14‧‧‧First capacitor

16‧‧‧second capacitor

18‧‧‧Second variable resistor

20‧‧‧buffered linear amplifier stage

22‧‧‧Buffered linear amplifier stage

24‧‧‧Bridge Peak Detector

26‧‧‧Bridge peak detector

28‧‧‧First Differential DC (d.c.) Amplifier

30‧‧‧Restricted amplifier stage

32‧‧‧Restricted amplifier stage

34‧‧‧ phase detector

36‧‧‧Second differential DC amplifier

38‧‧‧Total network

40‧‧‧Total network

Figure 1 is an illustration of a conventional technique for assuming equal amplitude quadrature signals of a local oscillator signal, but not ideal phase quadrature.

2 is a block diagram of an auto-orthogonal network in accordance with the present invention.

3 is an illustration of an orthogonal output from an auto-orthogonal network in accordance with the present invention.

Referring now to Figure 2, the local oscillator signal is input to a pair of paths (a path (RC) having a first variable resistor 12 in series with a grounded first capacitor 14, and a second capacitor 16 and a second grounded The other path (CR) of the variable resistor 18 is connected in series. The resistor/capacitor junctions of these respective paths are coupled to the inputs of the respective buffered linear amplifier stages 20, 22. The outputs from amplifier stages 20, 22 are input to respective diode peak detectors 24, 26 to detect the respective amplitudes of the signals output from the amplifier stages. The amplitude signals from the diode peak detectors 24, 26 are input to a first differential direct current (dc) amplifier 28 where the difference is a DC amplitude control signal (if the amplitudes are equal, then the DC The amplitude control signal is zero, or the DC amplitude control signal is based on which amplitude signal is larger, and is positive or negative.

After the respective amplifier stages 24, 26, these paths drive each The limiting amplifier stages 30, 32, whose outputs are the desired quadrature components (LO-I and LO-Q) of the LO input signal, are also input to the phase detector 34. The output from phase detector 34 is input to a second differential DC amplifier 36, the second input of which is coupled to ground to provide a DC phase control signal (if such phases are ideal phase quadrature, then the DC phase control The signal is zero, or if the phases are not ideal phase quadrature, the DC phase control signal is non-zero).

The DC control signals from the respective differential DC amplifiers 28, 36 are input to respective summing networks 38, 40, one for the adder and the other for the subtractor. The output from adder 38 controls the first variable resistor 12 at the input of the first path, and the output from subtractor 40 controls the second variable resistor in the second path that is connected to ground. When LO-I and LO-Q are equal amplitude and the ideal phase is orthogonal, the respective DC error signals at the inputs of the differential DC amplifiers 28, 36 are reduced to zero, and the DC control signals maintain their values.

In a "real world" environment, the RC and CR circuits of the respective orthogonal paths are not ideal, and the limiting amplifiers 30, 32 introduce their own phase errors as a function of the input amplitude. None of the familiar references (DaSilva or Chadwick) fully answer these questions. With only the Chadwick detector 34, it is not possible to concentrate on trying to maintain a fixed phase, while the RC/CR circuit wanders from one end of the adjustment range to the other. Finally, the RC/CR circuit is driven to one end of its range where it is unlikely to be recoverable. DaSilva locks the RC/CR circuit to a certain part because the amplitude is only balanced at a single frequency. However, even this However, there will be large phase errors that destroy the ideal phase quadrature, and these errors cannot be automatically corrected.

Figure 3 graphically shows the results of the network of Figure 2, which uses both amplitude and phase detection to automatically correct for any phase/amplitude error when any phase/amplitude error rises in the two orthogonal signal paths. Since the RC and CR circuits are automatically calibrated to be corrected, at the LO frequency (100 MHz in this example), the result is equal amplitude; and throughout the entire frequency range, the result is a fixed 90° phase relationship.

Accordingly, the present invention provides feedback by detecting the amplitude difference from the RC/CR circuit and the detected change from the ideal phase orthogonal between the orthogonal output signals (these differences and variations are provided together) The auto-control signal of the RC/CR circuit is calibrated to produce equal amplitude and ideal phase quadrature for the quadrature output signals, and an auto-orthogonal network with simultaneous amplitude and phase detection is provided.

12‧‧‧First variable resistor

14‧‧‧First capacitor

16‧‧‧second capacitor

20‧‧‧buffered linear amplifier stage

22‧‧‧Buffered linear amplifier stage

24, 26‧ ‧ diode peak detector

28‧‧‧First Differential DC (d.c.) Amplifier

30‧‧‧Restricted amplifier stage

32‧‧‧Restricted amplifier stage

34‧‧‧ phase detector

36‧‧‧Second differential DC amplifier

38‧‧‧Total network

40‧‧‧Total network

Claims (8)

An automatic orthogonal network for generating an output quadrature signal having equal amplitude and ideal phase quadrature for a desired frequency signal, the auto-orthogonal network comprising: a pair of orthogonal signal paths having the input as an input The desired frequency signal is used to generate a pair of temporary orthogonal signals at respective outputs, the pair of orthogonal signal paths comprising: an RC circuit having the desired frequency signal as an input, and having an output; and a CR circuit having The desired frequency signal is input and has an output; the amplitude detecting mechanism is configured to detect respective amplitudes of the temporary orthogonal signals to generate an amplitude control signal; and the phase difference detecting mechanism is configured to detect a phase difference between the temporary orthogonal signals to generate a phase control signal; and an combining mechanism for combining the amplitude control signal and the phase control signal to automatically generate respective orthogonal controls for calibrating the pair of orthogonal paths a signal such that the output orthogonal signals have equal amplitude and ideal phase orthogonality, and the combining mechanism includes: the amplitude control signal and the phase control signal An adding mechanism, configured to generate a first control signal of the RC circuit; and a subtracting mechanism of the amplitude control signal and the phase control signal for generating a second control signal of the CR circuit; thereby, the RC circuit and The CR circuit is automatically calibrated, and The output quadrature signals are of equal amplitude and ideal phase orthogonal. The automatic orthogonal network of claim 1, wherein the pair of orthogonal signal paths comprises: the RC circuit and the respective linear amplifier of the CR circuit, having respective ones coupled to the RC circuit and the CR circuit The inputs of the outputs are used to provide the temporary orthogonal signals at respective outputs of the linear amplifiers. The automatic orthogonal network of claim 2, wherein the amplitude detecting mechanism comprises: a first diode detector having one of the temporary orthogonal signals as an input for generating a first amplitude signal; a second diode detector having the other one of the temporary orthogonal signals as an input for generating a second amplitude signal; and the first amplitude signal and the second amplitude signal The combination mechanism is configured to generate the amplitude control signal at the output, where the amplitude control signal is a difference between the first amplitude signal and the second amplitude signal. The automatic orthogonal network of claim 3, wherein the phase difference detecting mechanism comprises: respective limiting amplifiers having inputs of respective temporary orthogonal signals coupled to receive the temporary orthogonal signals, For generating the output orthogonal signals at respective outputs; a phase detector having an input coupled to an output of the limiting amplifiers and having an output for generating a phase difference signal; and a comparator having The phase difference signal of the first input, and having The ground signal as the second input is used to generate the phase control signal at the output. An improved orthogonal network having RC orthogonal paths and CR orthogonal paths for generating quadrature output signals for frequency signals input to the respective paths; and having such paths from the respective paths An amplitude detecting mechanism for the orthogonal output signals for generating amplitude control signals for adjusting the respective paths to ensure equal amplitudes of the orthogonal output signals of the frequency signals of a specific frequency, the improvement comprising: a limiting mechanism, And limiting the amplitude of the orthogonal output signals to generate a quadrature output signal as a limit of the orthogonal output signals, the limiting mechanism comprising: a first limiting amplifier coupled to receive an output from the RC path Providing, as an input, a first limited quadrature output signal at an output of one of the inputs coupled to the phase detector; and a second limiting amplifier coupled to receive the CR path Outputting as an input to provide a second limited quadrature output signal at an output coupled to the other of the inputs of the phase detector, the first limited orthogonal The output signal and the second limited orthogonal output signal become the limited orthogonal output signals; the phase difference detecting mechanism is configured to detect a phase difference between the limited orthogonal output signals to generate phase control a signal, comprising a phase detector having the quadrature output signal as the input, and the phase control signal as an output; and an combining mechanism for combining the amplitude control signal and the phase Control Number to generate a control signal that automatically adjusts the combination of the respective paths to ensure equal amplitude of the quadrature output signals of the limits, and between the quadrature output signals of any of the frequencies of the frequency signal The ideal phase is orthogonal. An improved orthogonal network according to claim 5, wherein the combining mechanism comprises: a first combiner having the amplitude control signal from the amplitude detecting mechanism as input and the phase detector a phase control signal, and a control signal as a first combination of outputs, wherein the control signal of the first combination is a sum of the amplitude control signal and the phase control signal for adjusting the RC orthogonal path; and the second combiner, Having the amplitude control signal from the amplitude detecting mechanism as input and the phase control signal of the phase detector, and a control signal as a second combination of outputs, the control signal of the second combination is the amplitude control signal The difference between the control signal and the second combined control signal becomes the combined control signal to ensure the orthogonality of the constraints. The equal amplitude and ideal phase of the output signal are orthogonal. A method for automatically generating an orthogonal signal for a frequency signal, the orthogonal signal being equal amplitude and ideal phase orthogonal, the method comprising the steps of: inputting the frequency signal to a pair of orthogonal signal paths to be orthogonal thereto The respective outputs of the signal paths generate a pair of temporary orthogonal signals, wherein the pair of orthogonal signal paths includes: An RC circuit having the desired frequency signal as an input, and having an output; and a CR circuit having the desired frequency signal as an input, and having an output; detecting respective amplitudes of the temporary orthogonal signals, Generating an amplitude control signal; detecting a phase difference between the temporary orthogonal signals to generate a phase control signal; and combining the amplitude control signal with the phase control signal to automatically generate a calibration of the pair of orthogonal paths Orthogonal control signals, such that the output orthogonal signals have equal amplitude and ideal phase orthogonality, wherein the step of combining the amplitude control signal with the phase control signal comprises: the amplitude control signal and the phase control Adding signals to generate a first control signal of the RC circuit; and subtracting the amplitude control signal from the phase control signal to generate a second control signal of the CR circuit; thereby, the RC circuit and the CR circuit They are automatically calibrated such that the output quadrature signals have equal amplitude and ideal phase quadrature. The method of claim 7, further comprising the step of limiting the amplitude of the temporary orthogonal signals to generate an orthogonal signal as a limit of the temporary orthogonal signals for inputting the phase difference detecting step use.